A yogi (or yogin) is a term for a male practitioner of various forms of spiritual practice. In Hinduism it refers to an adherent of Yoga. The word is also often used in the Buddhist context to describe Buddhist monks or a householder devoted to meditation. The Shiva Samhita text defines the yogi as someone who knows that the entire cosmos is situated within his own body.
Yogini is the feminine form. Yoginis are known to possess a steadfast mind, which they cultivate through the disciplined pursuit of transcendence. Tantric scholars have described yoginis as independent, outspoken women with graceful spirits. Though the leaders of the modern Yoga-asana & meditation tradition have often been male, the vast majority of modern practitioners are female, including many who have attained mastery through the Yoga of the embodied Shakti mysteries of the life cycle and mothering. In the Hindu tradition, the the mother is first guru (teacher) and in the Yoga tradition, proper respect of Yoginis is a necessary part of the path to liberation. A Yogini is the sacred feminine force: the goddesses of mythology (Lakshmi, Durga, Kali).
Before you opt for a particular style of yoga, you should consider what you're looking for. Do you want strenuous exercises (stretching, muscle building, bodystiling) or relaxation (stress reduction, health, peace)? Sporting challenge you will find with Power Yoga, Ashtanga Yoga, Iyengar Yoga and Kundalini Yoga. Relaxation you can find in the normal Hatha Yoga and in the Vini Yoga.
Try out what is good for you. Ultimately, every yoga teacher's haas his personal style. Every yoga teacher has weaknesses and strengths. Learn from any yoga teacher. Find your own way to practice yoga. Take the best for you and accept in any yoga class the things that are personally not effective for you. And above all, always stay on your path of truth and accuracy. Don´t give up your mind on the door to spirituality.